This invention relates to a process for the preparation of fungicidally active cyclopentane derivatives.
EP-A2-0267778 discloses fungicidally active cyclopentane derivatives of the formula: ##STR5## or acid addition salts or metal complexes thereof, in which R.sup.1 and R.sup.2 each independently represents a C.sub.1-5 alkyl group or a hydrogen atom, each X represents a halogen atom, a C.sub.1-5 alkyl group or a phenyl group, n represents 0, 1 or 2 and A represents a nitrogen atom or a CH group, provided that R.sup.1 is not a hydrogen atom when R.sup.2 is a hydrogen atom.
GB-A1-2180236 discloses fungicidally active cyclopentane derivatives of the above formula in which R.sup.1 and R.sup.2 both represent hydrogen atoms, n represents an integer from 1 to 5, each X represents a hydrogen atom, a halogen atom, an alkyl group, a haloalkyl group, a phenyl group, a cyano group or a nitro group and A represents a nitrogen atom or a CH group.
The compounds disclosed in EP-A2-0267778 and GB-A1-2180236 exist in two stereoisomeric forms which have the following structures: ##STR6## The letters A and B will be used hereinafter to denote compounds having the same stereochemical configuration as isomers A and B above.
Isomers A and B can be separated by, for instance, chromatography and exhibit different fungicidal activity. Generally, isomers of the formula A exhibit greater fungicidal activity than isomers of the formula B.
The processes for the preparation of the above compounds disclosed in GB-A1-2180236 and EP-A2-0267778 produce a mixture of isomers of the formulae A and B thereby necessitating the inclusion of an isomer separation step in the process. Moreover, production of the more active isomer A is not maximised in such processes because a portion of the starting materials is consumed in the simultaneous generation of the less active isomer B. However, a new process has now been discovered for the preparation of such compounds which is highly stereospecific in favour of the more active isomer A.